Rudi Giuliani, mayor of New York (1993-2002): during his tenure, crime in the city fell dramatically, though the trend did pre-date his mayoralty and has continued since. Photograph: AP Photo/Gino Domenico

Nothing stirs up the American policymaking community like talking about crime. This is understandable when crime skyrockets, but anxiety levels have remained high even as America's crime rate has descended to its lowest level in 40 years. Scholars and wonks rush so quickly to claim credit – as quickly as they seek refuge to avoid blame – that getting to the core of the problem is not so easy. But when you leave aside the politicking, you find that it's actually more important to understand community responses to crime, rather than to figure out exactly how or why crime persists.

But fads are not easy to ignore. Consider the latest intellectual fashion that links imprisonment with reductions in crime rates. Simple enough in principle, but is it truthful (or just "truthy")? The chief proponent, besides US police and sheriff associations, is public policy Professor James Wilson, who argues that lengthier penal sentences keeps potential criminals behind bars.

In the other corner, groups like the Sentencing Project beg to differ, with some nifty statistics to prove their point (pdf) – for example, that the states where imprisonment was below the national average experienced the greatest drops in crime. It would be silly to ignore the positive effects of incarceration – some offenders do tend to transgress repeatedly over the life course, so keeping them off the streets is smart. But, it is equally foolhardy to think that incarceration is the always best answer. Canada, for instance, has much lower incarceration rates than the US, yet its crime rate is also low.

The problem is making generalisations across all crimes and across all US cities and states. Criminologists still really don't understand why Chicago's youth homicide rate went through the roof last year, while New York's stayed at a near-historic low. My colleague, "Freakonomics" economist Steven Levitt, shows that changing drug habits can affect some crimes but not others: homicides dropped after the early 1990s as crack became less popular, but other crimes did not.

Instead of studying why crime occurs, we should instead be looking at the capacity of communities to take action against it. Local public safety depends on the locals who can respond to criminal and delinquent acts before they destroy the social fabric. No region in America is free from social problems, but communities differ widely in terms of the capacity among citizens to respond. Recent research suggests that rather than fighting criminals directly, it may be as advantageous to help communities fight against crime. As we champion our favourite deterrents – prisons on the right, job growth on the left, we may want to remember that an active citizenry, able to defend itself, is a proven ingredient for ensuring public safety.

Tracey Meares, Yale University's renowned legal scholar, has demonstrated the power of "take back the night" vigils and protests for warding off criminals, especially when religious leaders lead the crusade and bring police aboard. Social scientists at Harvard argue that the best predictor for low crime rates is the "collectively efficacious" behaviour of residents – a fancy phrase that refers to the ability of neighbours to work together when things go awry. And David Kennedy has shown proven results with his "Ceasefire" programme, which focuses on issuing real threats to criminals, with consequences that are delivered swiftly.

Such efforts fall under a large umbrella called "community policing", which took off in the 1990s – and in Europe, the decade after. President Clinton helped cities hire 100,000 cops. Urban mayors from Chicago to Seattle to New York built local coalitions of residents, businesspersons, clergy, school principals and other so-called "stakeholders" who could respond to crime before it spiralled out of control.

The power of such coalition-style policing lies in the phalanx of crime fighters that confronts local criminals: not only do the perps feel the weight of the law around them, but they come to believe that law enforcement is sincere when it threatens to lock up criminals. In short, truth in advertising has proven to be an excellent deterrent to crime.

But "community policing" is subject to interpretation – and not surprisingly, left and right differ in predictable ways. Advocates of gun rights are quick to call for the need for relaxed weapons laws, while those on the left want community organisations to become even more empowered with federal funding and services.

Don't expect any of these debates to get settled soon. Instead, I'd recommend a simple exercise when the next theory about crime rates makes headlines. Ask yourself, what do communities do when crime occurs? Can they act "efficaciously"? Or are they held hostage by gangs, car thieves, vandals and other criminals? We may never understand with great precision what causes crime, but we can always empower citizens to respond when it occurs.

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